Charles Sykes/Bravo(NEW YORK) -- Martha Stewart's sister, Laura Kostyra Plimpton, has died of a massive brain aneurysm. She was 59 years old.

Stewart, 73, wrote on her blog that that the death Plimpton, the youngest of her five siblings, was unexpected. On Monday morning, she woke up early to work out and make coffee for her husband, Randy. After working on a crossword puzzle, she took a shower and complained that she felt unwell.

"She was rushed to the hospital where they said she had suffered a massive brain aneurysm. Laura left a living will so she was kept on life support until today so her three children could say their goodbyes, and the testing could be completed for organ donation," she wrote in a blog post Wednesday. "We are so sad but also happy that Laura had the foresight to donate so many healthy organs to needy people."

Stewart, who added that Plimpton worked for her company for more than 25 years, asked that readers keep her family in their thoughts, specifically Randy and Plimpton's three children and two sons-in-law.

"Laura deserves the very best," she concluded. "She was an extraordinary mother, wife, and sister."